I have a 92 f150 4 x 2 and I found some chrome mickey thompsons, I'm just worried they won't fit right or something. I have no lift or anything, stock suspension. I have 31x 10.50 on the factory rims with no problems. I wanna up grade to 15 x 8 rims with a 3.31 backspace and a -30 mm offset. Any problems or concerns?

I'm really trying to widen the stance of my truck with the 31's cuz there pretty much new. So any other ideas our suggestions would be appreciated as well. And pics of them would be even better.

 

Will they fit? If the bolt pattern and the center hole match the stock rims then, yes.

Will they be fine? That depends. the rims are 1/2" wider than stock but you won't see all of that in the tires, they will probably be somewhere around 3/8" wider of which half or about 3/16" will be to the outside. The stock rims are either zero offset or very close to it. By going to -30 offset rims you are moving each tire outwards about 1-3/16" so the end result is that each tire is 1-3/8" further out than what you have now or 2-3/4" wider overall. That should not present any fender clearance issues but you need to check to make sure.

There is still the problem of increased load on your steering linkage and especially on your ball joints. If you increase the distance between the wheel centerline and what is called the kingpin axis (an imaginary line drawn through the centers of the ball joints) you necessarily increase the load on those joints and decrease their life. There is no way around this. Even if you are willing to accept the probability of premature failure, you need to consider the possibility of catastrophic failure.

 

Yeah I was more than sure there would be a negative outcome from this. But was praying it wouldnt be a problem. Would rims with a 4 inch backspace and -13 offset be safer?

 

Absolutely. That's about the same backspace as the stock rims so you're taking all the additions to the outside. However, will only amount to about a 1-3/8" increase in your overall width which is not what you wanted.

 

Yeah I was really hoping to go with some low backspaced rims so they coils stick out, but if it might cause problems as you suggested it's really not worth it. What do you think would be the lowest backspace I could go, without causing problems?

 

Although the two measurements are very closely related, it's not backspace, it's offset that matters when it comes to suspension loads. I've got 255/70-16 tires on 8" zero offset rims. They're 3/4" wider than stock but no change in wheel centerline, no reduction in wheel strength, no changes in ball joint loads, no changes in steering geometry and only minor increases in the loads on the steering joints.

The closer you can come to zero offset, the better off you will be. The problem is that as wheel width increases, you need more offset to keep the backspace to something near stock so that the wheels don't interfere with the suspension.

 

So pretty much it's the offset that can effect it? So it doesn't matter how low of a backspace I go with, as long as my offset stays near 0?

 

If you maintain the offset but increase the backspace, you will necessarily increase the rim width

Do you understand how the two numbers are interrelated?
Look at post #6 in this thread
https://www.f150online.com/forums/pr...heel-help.html
I explained them as best that I can

The physical limit on backspace is probably somewhere around 5" or 5-1/2". My wheels are at 4-1/2" and they're getting close to hitting things. They'd be even closer if they were 15". The only real way to tell is to trial fit.

With 31 x 10.50 -15 tires, the tire manufacturers generally state that you don't want to go above a 9" rim. Since 9" rims are around 10" wide outside dimension a 9" zero offset rim would have roughly a 5" backspace. I don't think you're going to find such a rim though.

The 8 x 15 rims with -13 offset are probably as close as you're going to get and still be able to pick up some overall width. You might find something in an 8.5" rim width that comes a little closer.

Is it really worth the effort??

 

Well I've seen some 15 x 8 with backspace ranging from 3.75 to 2.5. I get how they work and stuff, I just want to know if I keep the same width, 15 x 8, but got the backspace low and kept the same offset roils that be okay?

 

What you want to do is impossible. For any given wheel width if you swap to a rim with reduced backspace, you will necessarily increase the negative offset. They're simply two different ways of measuring the same thing. It's just that offset is more useful for looking at loads and steering geometry whereas backspace is more useful for looking at suspension clearance.

 

Okay thanks for all your help, and sorry if I made you repeat yourself out frustrated you haha I'm new to all this.

 

Thank you!!!!!! I've always wondered about backspace and offset and never really knew how much it mattered.

 

Here's a pair of diagrams
https://www.rsracing.com/tech-wheel.html#backspace